RDS, or as we say in Canada, RDBS ("Radio Data Broadcast System") is a low-cost technique to provide many of the value-added services associated with Digital Radio to existing FM stations.  Like Eureka DAB, it's been around for a while, and has proven to work as advertised.  Unlike DAB, there are lots of RDS-equipped radios already available to the public, which makes some of us wonder why it hasn't caught on like sliced bread, at least so far.


RDS is a narrow-band data subcarrier that operates at 57 kHz, which is exactly the third harmonic of the 19 kHz stereo pilot.  The 57 kHz carrier is suppressed, leaving only the data sidebands, which are typically injected at 4% or so of total modulation.


The data provided can be a little or a lot.  At the low end, most stations would implement scrolling call letters and a station slogan.  RDS can also tell the receiver what format the station thinks it is, and can provide accurate time, so receivers can be programmed to seek, say, country music radio stations, and always have accurate time displayed.  Many stations like to add scrolling song title and artist information, both for what's playing right now and what's coming up after the next stop set ends.  Some stations in Seattle (where RDS installation has been quite active) also put up weather forecast information and ski patrol info at the same time that they're announcing it.


A unique feature of RDS-equipped car radio/CD players is the ability to set a data flag when local traffic information is being discussed on the main channel.  This flag can tell the radio to interrupt a CD that it's playing (or another radio station), switch to the traffic info, then switch back after the report is finished.


Another DAB-like feature of RDS is the ability to provide lists of alternate frequencies where the station may be found in areas where the primary frequency is weak or unavailable.  The receiver can be set up to switch automatically to the alternate frequency when this happens.  This would seem to be a natural feature for CBC/Radio Canada, yet they, too, have been slow to adopt the technology.


Like Eureka DAB, RDS comes to us from Europe (France and Germany).  RDBS, the North American flavour, is very similar to RDS, and receivers equipped for one standard have little trouble with the other.  The concept seems to be much more popular in Europe, with the majority of radio stations and receivers conforming to at least part of the standards.


One of the few controversial aspects of the system is whether or not song information should be scrolling across the faceplates of car radios.  Expressly forbidden in Europe, it is perhaps the most attractive aspect of RDBS for North American stations and listeners.  The Europeans fear that the scrolling data will distract drivers and cause accidents.  Surprisingly enough, we never heard a similar argument when DAB was displaying similar features; now that very dynamic GPS, MP3 and DVD displays also are on dashboards, the point may well have been rendered moot.


So why don't we hear more about RDS, and why haven't more radio stations jumped on the bandwagon?  It's available to any FM radio station out there, and the entry-level encoders, that provide the scrolling "static" information can be purchased for less than $1,000.  Even the more sophisticated "dynamic RDS encoders" cost only a few thousand dollars to install.  (But it may be quite a bit more involved to provide automatic song titling information, for instance, depending upon your existing automation system.)  Perhaps the problem is a lack of awareness of the number of RDS-equipped receivers already in the market.  Although we've heard some estimates of as high as 1/3 of aftermarket car radios being RDS-equipped, very few choose to brag about it.  You'll see radios advertising features such as MP3 capability or detachable face plates, but it can be very hard to find out if a radio is RDS-equipped without actually trying it out yourself.  This is also true of factory-equipped radios in new vehicles.


It's possible that RDBS, rather than making a big splash, is going to silently sneak up on us all, gradually gaining market share until we're wondering how we got along without it.